TT is telling me that itemizing deductions is best for me. But itemized deductions total $18,245. I'm married filing jointly, so isn't my standard deduction higher?

You can check the actual amount of itemized deductions by using the Search Topics for "itemized deductions, choosing" (under "My Account, Tools" in the online versions). Click on "Change my deduction". That will display the actual amount of itemized deductions vs. the standard deduction. (Be sure to uncheck "Change my deduction" after checking it so you do not lock in the wrong deduction.

2020 standard deductions

$12,400 Single
$18,650 Head of Household
$24,800 Married Jointly

Add an additional $1,300 for over age 65 or blind
This amount increases to $1,650 if the taxpayer is also unmarried.

Are you looking at your gross deductions?  Not all count at 100%.  The total of property/state/local taxes is capped at $10,000.  And only the amount of Medical that is in excess of 7.5% if AGI qualifies.